The transmitter used by BH is commerically built in Germany by ID-Elektronik
 http://www.id-elektronik.de/
 it is completely ready for use and has the following specs

Frequency range:	2320 - 2450
Output:	1.5 W
Voltage supply:	12 - 15 V DC
RF Out:	N socket
Video in:	Phono
RF in:	N socket
12V Supply:	4 pole DIN
Supply inclusive. Voltage supply cable and documentation
Dimensions:	225 x 175 x 55 mm